Phytate is the major but indigestible form of phosphorus found in plant-based feeds. It is considered as an anti-nutritional factor (ANF) that needs to be reduced or removed from cereal-based foods and feeds. Under acidic conditions, phytate interacts with positively charged dietary proteins leading to the formation of phytate-protein aggregates and precipitates, which results in a decreased accessibility for proteases, and consequently in inefficient protein digestion. Phytate also acts as a strong chelating agent that binds different vital metal ions in foods and feeds in the small intestine of monogastric organisms, leading to nutritional deficiencies of many important minerals like calcium, zinc, etc. in animals.
Phytase is a phosphatase that catalyzes the hydrolysis of O—P bonds in phytate and releases inorganic usable phosphorous. Phytase plays versatile roles in agricultural and feeding fields. Ruminant animals such as cattle and sheep can utilize the phytate in grains as a source of phosphorus since they have bacteria in the gut that produces phytases. Non-ruminants like pigs, poultry, fish, dogs, birds, etc. require extrinsic phytase to liberate inorganic phosphorous. Hence, addition of inorganic phosphorous, a non-renewable and expensive mineral, to feeds for monogastric animals is a common practice, which incurs heavy costs to the feed industry. Consequently, phytase produced from various sources have emerged as one of the most effective and lucrative supplement to these species' diets to enhance the nutritional value of animal feeds and decrease animals' phosphorus excretion that leads to environmental pollution.
Phytase in feeds can be inactivated by temperature during feed processing (pelleting), by the low pH or pepsin in the upper part of the gastrointestinal tract of an animal. Selle and Ravindran laid out the characteristics for an ideal feed enzyme, namely; 1) a high specific activity per unit of protein, 2) good thermostability during feed processing, 3) high activity in the typical pH range of the animal gut, 4) resistance to gastric proteases, and 5) good stability under ambient temperatures. (SELLE, P. H. and RAVINDRAN, V. (2007) Microbial phytase in poultry nutrition. Animal Feed Science and Technology 135: 1-41.)
The heat treatment of feeds can involve heat alone or a combination of both heat and pressure. The most common form of thermal treatment in the manufacture of poultry feeds is pelleting. The pelleting process first involves the mash feed passing through a conditioner. In the conditioner the cold feed is exposed to dry steam which is added under pressure. This process helps to improve pellet durability and also increases mill throughputs and reduces energy consumption. Under these conditions, plant cells are crushed, which is favorable for the digestion process in animals. Nissinen found that moderate conditioning less than 85° C. was optimal for broiler performance and high conditioning temperature at 95° C. resulted in poorer body weight gain and feed conversion ratio (NISSINEN, V. (1994) The effects and interactions of enzymes and hydrothermal pre-treatments and their contribution to feeding value. International Milling Flour and Feed, May: 21-22.). Pelleting process at 65-85° C. usually result in improving the availability of nutrients due to the rupture of the cell wall matrix (PICKFORD, J. R. (1992) Effects of processing on the stability of heat labile nutrients in animal feeds, in: GARNSWORTHY, P. C., HARESIGN, W. & COLE, D. J. A. (Eds) Recent Advances in Animal Nutrition, pp. 177-192 (Butterworth-Heinemann, Oxford, U.K.) and deactivation of enzyme inhibitors present in cereals (SAUNDERS, R. M. (1975) α-Amylase inhibitors in wheat and other cereals. Cereal Foods World 20: 282-285.). The effect of the damage on the phytase activity due to high pressure appears to be small; it is mainly the high temperature which results from the high energy input that inactivates the enzyme. Thus, developing a thermostable Phytase provides an attractive solution for cost-effective processes in the feed industry.
New applications of phytase in human foods are similarly important as those in animal feeds because indigestible phytate chelates essential minerals and contributes to deficiencies of these nutrients in approximately two to three billion people. The applications of phytase in human health and medicine represent other new exciting areas. In addition, phytase has great potentials for industrial applications including food processing and biofuel production. Thermostable phytase, along with xylanase, have been suggested as effective additives in the pulp and paper industry.